In compact disc fabrication, a glassmaster ("glass") is used to generate patterns that will used later in the CD manufacturing process to stamp the CD's themselves. Thus, the accuracy of the pits and lands on the glass will ultimately determine the quality of the CD's.
One of the most common methods for creating CD's is a stamper-injection molding process. In this method, a glass master is coated with a photoresist layer, and the layer is developed using a laser to create the pit geometry that holds the data in the CD. The glass is then used to form stampers for stamping the CD's out of transparent polycarbonate or a similar material. The CD's are then coated with a thin reflective metal layer and then a protective acrylic layer.
Before the CD's are actually stamped, however, the accuracy of the glassmaster must be checked using an orders measurement device. The device measures the pit geometry on the glass by focusing a laser beam on the glass and measuring the orders of diffraction resulting from the laser beam being refracted and reflected by the pits as the glass is rotated. The minuscule dimensions of the pits on the glass require that the glass be held securely in place as laser beams are directed through it; any erroneous movement of the glass during the scanning process will cause a misreading.
Many glasses, such as those used by Philips, have a hub attached to the center of the glass with adhesive, and this type of glass is normally loaded onto a rotation spindle in the orders measurement device so that the spindle extends through the hub to anchor the glass in place as it is being checked by the device. Because the hub is permanently attached to the glass, the hub and the glass are kept concentric with respect to each other for accurate scanning.
Not all glasses have a hub in the center to accommodate the spindle in the orders measurement device, however. In fact several companies use hubless glasses, which are essentially flat glass discs with no center hubs glued to the surface. Without the hub, there has been no known way to mount the glass on the spindle of the orders measurement device. Although it is possible to use adhesive to attach hubs to the hubless glasses, this process can become time-consuming and add unnecessary manufacturing steps.
It is therefore an object of the present invention to construct a device that allows hubless glassmasters to be mounted on a spindle of an orders measurement system that is specifically designed for testing hubbed glasses without altering the basic structure of the hubless glass.